US7185964B2 - Printing method and printing apparatus - Google Patents

Printing method and printing apparatus Download PDF

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Publication number
US7185964B2
US7185964B2 US10/784,262 US78426204A US7185964B2 US 7185964 B2 US7185964 B2 US 7185964B2 US 78426204 A US78426204 A US 78426204A US 7185964 B2 US7185964 B2 US 7185964B2
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Prior art keywords
printing
pixel
dot layout
assigned
pattern
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US20040165022A1 (en
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Hidehiko Kanda
Takeji Niikura
Tetsuya Saito
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Canon Inc
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Canon Inc
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
    • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
    • B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
    • B41J2/01—Ink jet
    • B41J2/205—Ink jet for printing a discrete number of tones

Definitions

  • This invention relates to a printing method and printing apparatus and, more particularly, to a printing method and printing apparatus which print using an inkjet printhead.
  • Printing apparatuses used as a printer, a copying machine, a facsimile apparatus, or an output apparatus for a multifunction electronic apparatus or work station including a computer or wordprocessor print images (including characters and the like) on printing media such as a printing sheet and thin plastic plate on the basis of image information (including character information and the like).
  • Such printing apparatuses can be classified by the printing method into an inkjet method, wire dot method, thermal method, electro-photographic method, and the like.
  • a printing apparatus complying with the inkjet method (to be referred to as inkjet printing apparatuses hereinafter) prints by discharging ink from a printhead onto a printing medium.
  • the inkjet printing apparatus easily achieves high definition, high speed, quiet operation and low cost.
  • the integration of ink orifices and liquid channels serving as ink discharge portions is adopted in a printhead formed by integrating and arraying a plurality of printing elements.
  • a plurality of printheads are mounted to the apparatus.
  • a dot layout pattern corresponding to the gradation levels (also referred to as “quantization levels”) of pixels is assigned.
  • the gradation level includes not only a halftone level of achromatic color but also a halftone level of chromatic color (e.g. cyan, magenta and yellow).
  • Japanese Patent Publication Laid-Open No. 9-46522 discloses a method of assigning plural types of dot layout patterns to a plurality of pixels at the same gradation level (quantization level). In this arrangement, dots are laid out at different intervals within a region formed by a plurality of pixels at the same gradation level, resulting in a noise-added printing state.
  • the present invention is conceived as a response to the above-described disadvantages of the conventional art.
  • a printing method and a printing apparatus using the method according to the present invention are capable of printing a high-quality image free from any visual graininess while sufficiently reducing density unevenness and color unevenness.
  • a printing method of printing by discharging ink from a printhead onto a printing medium on the basis of a dot layout pattern corresponding to a gradation level of each pixel comprises: a selection step of selecting one printing operation mode from a first printing operation mode in which one dot layout pattern is assigned to a plurality of pixels at the same gradation level and printing is done on the basis of the assigned dot layout pattern, and a second printing operation mode in which plural types of dot layout patterns are assigned to a plurality of pixels at the same gradation level and printing is done on the basis of the assigned dot layout patterns; and a printing step of executing the printing operation mode selected in the selection step.
  • a printing method of printing by discharging ink from a printhead onto a printing medium comprises: a determination step of determining a dot layout pattern to be assigned to each pixel in accordance with at least one information out of information on a size of the printing medium and information on a size of image data; and a printing step of printing each pixel on the basis of the determined dot layout pattern, wherein the determination step determines whether to assign one dot layout pattern or plural types of dot layout patterns to a plurality of pixels at a predetermined level in which a predetermined number of dots are printed in accordance with the at least one information.
  • one type of dot layout pattern assigned to the pixels at the predetermined level may include a pattern for printing dots at the same position within the pixel, and the plural types of dot layout patterns assigned to the pixels at the predetermined level may include a pattern for printing dots at different positions within the pixel.
  • the plural types of dot layout patterns assigned to the pixels at the predetermined level may also include a pattern for printing dots at different positions within the pixel, and a pattern for printing dots at the same position within the pixel.
  • the present invention may also be realized by applying the method having the above steps to a printing apparatus.
  • the printing apparatus has the following arrangement.
  • a printing apparatus which prints by discharging ink from a printhead onto a printing medium on the basis of a dot layout pattern corresponding to a gradation level of each pixel, comprises:
  • first printing means for executing a first printing operation mode in which one dot layout pattern is assigned to a plurality of pixels at the same gradation level and printing is done on the basis of the assigned dot layout pattern; and second printing means for executing a second printing operation mode in which plural types of dot layout patterns are assigned to a plurality of pixels at the same gradation level and printing is done on the basis of the assigned dot layout patterns.
  • the printing apparatus may also have the following arrangement.
  • a printing apparatus which prints by discharging ink from a printhead onto a printing medium on the basis of a dot layout pattern corresponding to a gradation level of each pixel, comprises:
  • first printing means for executing a first printing operation mode in which one dot layout pattern is assigned to a pixel corresponding to a predetermined gradation level out of a plurality of gradation levels and printing is done on the basis of the assigned dot layout pattern; and second printing means for executing a second printing operation mode in which plural types of dot layout patterns are assigned to a pixel corresponding to the predetermined gradation level and printing is done on the basis of the assigned dot layout patterns.
  • the printing apparatus may also have the following arrangement.
  • a printing apparatus which prints by discharging ink from a printhead onto a printing medium, comprises: first printing means for executing a first printing operation mode in which a dot layout pattern for printing dots at the same position within a pixel is assigned to a pixel corresponding to a predetermined gradation level out of a plurality of gradation levels and printing is done on the basis of the assigned dot layout pattern; and second printing means for executing a second printing operation mode in which plural types of dot layout patterns including a dot layout pattern for printing dots at different positions within the pixel are assigned to a pixel corresponding to the predetermined gradation level and printing is done on the basis of the assigned dot layout patterns.
  • the printing apparatus may also have the following arrangement.
  • a printing apparatus which prints by discharging ink from a printhead onto a printing medium, comprises: determination means for determining a dot layout pattern to be assigned to each pixel in accordance with at least one information out of information on a size of the printing medium and information on a size of image data; and printing means for printing each pixel on the basis of the dot layout pattern determined by the determination means, wherein the determination means determines, in accordance with the at least one information, whether to assign one dot layout pattern or plural types of dot layout patterns to a plurality of pixels at a predetermined level in which a predetermined number of dots are printed.
  • a more detailed arrangement preferably further comprises scanning means for reciprocally scanning the printhead in a first direction (main scanning direction), and conveyance means for conveying the printing medium in a second direction (sub-scanning direction) different from the first direction
  • the size of the printing medium preferably includes at least any one of a size in the first direction, a size in the second direction, and a sum of the sizes in the first and second directions
  • the size of the image data preferably includes at least any one of a size in the first direction, a size in the second direction, and a sum of the sizes in the first and second directions.
  • the printing means preferably includes multi-pass printing control means for controlling so as to scan a region printable by one scanning using all printing elements of the printhead by the printhead plural number of times, thereby completing printing in the region.
  • the above-mentioned single dot layout pattern assigned to the pixels at the predetermined level preferably includes a pattern for printing dots at the same position within the pixel, and the plural types of dot layout patterns assigned to the pixels at the predetermined level preferably include a pattern for printing dots at different positions within the pixel.
  • the plural types of dot layout patterns assigned to the pixels at the predetermined level preferably include a pattern for printing dots at different positions within the pixel, and a pattern for printing dots at the same position within the pixel.
  • dots are preferably printed at the different positions by changing a dot position in a first direction in which the printhead is scanned by the scanning means.
  • ink droplets are preferably printed at the different positions by changing a dot position in a second direction in which the printing medium is conveyed by the conveyance means.
  • the invention is particularly advantageous since a high-quality image almost free from graininess can be printed while density unevenness is suppressed.
  • FIG. 1 is a perspective view schematically showing the whole arrangement of an inkjet printing apparatus as a typical embodiment of the present invention
  • FIG. 2 is a view showing ink orifices arrayed in a printhead 102 when viewed from the z direction;
  • FIG. 3 is a block diagram showing the control arrangement of the printing apparatus shown in FIG. 1 ;
  • FIG. 4 is a view showing the layout of the ink orifices of a printhead 102 according to a first embodiment
  • FIG. 5 is a table for explaining the relationship among the quantization level of image data, the number of printing dots, and pixel data according to the first embodiment
  • FIG. 6 is a view for explaining the first printing operation according to the first embodiment
  • FIGS. 7A , 7 B, and 7 C are views for explaining a dot layout within one pixel at a resolution of 600 ⁇ 600 dpi for pixel data printed by printing operation shown in FIG. 6 ;
  • FIGS. 8A , 8 B, 8 C, and 8 D are views each showing the dot distribution of 2 ⁇ 2 pixels printed by the first printing operation at each quantization level;
  • FIG. 9 is a view for explaining the second printing operation according to the first embodiment.
  • FIGS. 10A , 10 B, and 10 C are views for explaining a dot layout within one pixel at a resolution of 600 ⁇ 600 dpi for pixel data printed by printing operation shown in FIG. 9 ;
  • FIGS. 11A , 11 B, 11 C, and 11 D are views each showing the dot distribution of 2 ⁇ 2 pixels printed by the second printing operation at each quantization level;
  • FIG. 12 is a table showing the relationship among the main scanning sizes of printing media printed by the first and second printing operations, density unevenness in the main scanning and sub-scanning directions, and graininess;
  • FIG. 13 is a flow chart showing printing control according to the first embodiment
  • FIGS. 14A , 14 B, and 14 C are views for explaining a printing dot layout within each printing pixel on a printing medium when printing is done according to a first modification to the first embodiment
  • FIGS. 15A , 15 B, 15 C, and 15 D are views each showing the dot distribution of 2 ⁇ 2 printed pixels at each quantization level according to the first modification to the first embodiment
  • FIG. 16 is a table showing the relationship among the sub-scanning size of the printing medium, density unevenness in the main scanning and sub-scanning directions, and graininess according to a second modification to the first embodiment;
  • FIG. 17 is a table showing the relationship among the sum of the main scanning and sub-scanning sizes of the printing medium, density unevenness in the main scanning and sub-scanning directions, and graininess according to the second modification to the first embodiment;
  • FIG. 18 is a table showing the relationship among the main scanning sizes of images printed on printing media by the first and second printing operations, density unevenness in the main scanning and sub-scanning directions, and graininess;
  • FIG. 19 is a flow chart showing printing control according to the second embodiment.
  • FIG. 20 is a table showing the relationship among the sub-scanning size of an image printed on a printing medium, density unevenness in the main scanning and sub-scanning directions, and graininess according to a modification to the second embodiment;
  • FIG. 21 is a table showing the relationship among the sum of the main scanning and sub-scanning sizes of an image printed on a printing medium, density unevenness in the main scanning and sub-scanning directions, and graininess according to another modification to the second embodiment.
  • FIG. 22 is a view showing a modification to the orifice layout of the printhead.
  • the terms “print” and “printing” not only include the formation of significant information such as characters and graphics, but also broadly include the formation of images, figures, patterns, and the like on a print medium, or the processing of the medium, regardless of whether they are significant or insignificant and whether they are so visualized as to be visually perceivable by humans.
  • the term “print medium” not only includes a paper sheet used in common printing apparatuses, but also broadly includes materials, such as cloth, a plastic film, a metal plate, glass, ceramics, wood, and leather, capable of accepting ink.
  • ink (also referred to as “liquid”) should be extensively interpreted similar to the definition of “print” described above. That is, “ink” includes a liquid which, when applied onto a print medium, can form images, figures, patterns, and the like, can process the print medium, and can process ink (e.g., can solidify or insolubilize a coloring agent contained in ink applied to the print medium).
  • nozzle generally means a set of a discharge orifice, a liquid channel connected to the orifice and an element to generate energy utilized for ink discharge.
  • FIG. 1 is a perspective view schematically showing the whole arrangement of an inkjet printing apparatus (to be referred to as a printing apparatus hereinafter) as a typical embodiment of the present invention.
  • a carriage 106 which reciprocates in the x direction (main scanning direction) supports an ink cartridge comprised of a printhead 102 and ink tanks 101 which store four color inks: black (K), cyan (C), magenta (M), and yellow (Y) inks.
  • K black
  • C cyan
  • M magenta
  • Y yellow
  • a conveyance roller 103 and auxiliary roller 104 rotate in directions indicated by arrows shown in FIG. 1 while clamping a printing medium P. Every time printing of one scanning by the printhead 102 is completed, the printing medium P is conveyed in the y direction (sub-scanning direction). At the start of printing, paper feed rollers 105 feed the printing medium P, and also clamp it, similar to the conveyance roller 103 and auxiliary roller 104 .
  • the carriage 106 moves to a position (home position (h)) represented by a dotted line in FIG. 1 , and stands by at this position.
  • FIG. 2 is a view showing ink orifices arrayed in the printhead 102 when viewed from the z direction.
  • reference numeral 201 denotes a plurality of orifices arrayed in the printhead 102 .
  • the carriage 106 is at the home position h in FIG. 1 before the start of printing.
  • the printing apparatus receives a printing start instruction from a host (not shown)
  • the carriage 106 discharges ink onto a printing medium P from the orifices 201 of the printhead 102 and prints in accordance with received printing data while moving in the x direction.
  • the carriage 106 returns to the original home position h. During the period of this return, the printing medium P is conveyed by a printing width corresponding to one scanning by the printhead in the y direction. After that, the carriage 106 again moves in the x direction to print.
  • FIG. 3 is a block diagram showing the control arrangement of the printing apparatus shown in FIG. 1 .
  • the control arrangement of the printing apparatus is roughly divided into a data processing subsystem including: an image input unit 303 ; a corresponding image signal processing unit 304 ; and a CPU 300 , and a mechanism control processing subsystem including: an operation unit 306 ; a recovery system control circuit 307 ; a head temperature control circuit 314 ; a head driving control circuit 315 ; a carriage driving control circuit 316 ; and a conveyance control circuit 317 .
  • These units respectively access a main bus line 305 .
  • the image input unit 303 comprises an interface for inputting printing data from a host computer (not shown); an interface for inputting image data from a digital camera (not shown); and an interface for inputting image data from an IC memory card (not shown).
  • the CPU 300 comprises memories such as a ROM 301 and RAM 302 .
  • the CPU 300 gives proper printing conditions for input information, and drives the printhead 102 to print.
  • the RAM 302 stores in advance a program for executing a head recovery timing sequence. If necessary, recovery conditions such as preliminary discharge conditions are supplied to the recovery system control circuit 307 , the head driving control circuit 315 , and the like.
  • a recovery system motor 308 drives the printhead 102 , and a cleaning blade 309 , a cap 310 , and a pump 311 which face the printhead 102 at intervals.
  • the head driving control circuit 315 executes a sequence according to the driving conditions of the printing elements (electrothermal transducers) of the printhead 102 . In general, the head driving control circuit 315 causes the printhead 102 to perform ink preliminary discharge and printing ink discharge.
  • a heater 313 is arranged on a substrate having the printing elements of the printhead 102 .
  • the ink temperature in the printhead can be adjusted to a desired setting temperature.
  • a diode sensor 312 is similarly arranged on the substrate, and measures an actual ink temperature in the printhead.
  • the diode sensor 312 may be arranged on the substrate, similar to the heater 313 , but may be arranged outside the substrate or around the printhead.
  • FIG. 4 is a view showing the layout of the ink orifices of a printhead 102 according to a first embodiment. As described above, any one of black (K), cyan (C), magenta (M), and yellow (Y) inks is discharged from the ink orifices.
  • K black
  • C cyan
  • M magenta
  • Y yellow
  • n 1 to n 8 shown in FIG. 4 represent nozzle numbers, and the size of an ink droplet from each ink orifice is about 5 pl.
  • Each ink orifice incorporates a corresponding printing element (electrothermal transducer).
  • FIG. 5 is a table for explaining the relationship among the quantization level (gradation level) of image data, the number of printing dots, and pixel data according to the first embodiment.
  • image data is multi-valued image data having a resolution of 600 ⁇ 600 dpi per pixel, and is quantized to five levels from 0 to 4. More specifically, image data is 4-bit data (to be referred to as pixel data hereinafter) corresponding to the quantization level.
  • This quantization may be executed by an image signal processing unit 304 after multi-valued image data is input to an image input unit 303 , or input image data may be quantized data in order to reduce the load on the printing apparatus.
  • 4-bit pixel data has six types: “0011”; “0101”; “0110”; “1001”; “1010”; and “1100” at which any two bits are ON.
  • pixel data to be printed is selected in accordance with the quantization level, and ink droplets are discharged and printed in a lattice at a resolution of 600 ⁇ 600 dpi.
  • quantization level quantization level 1 , 2 , or 3
  • one of the bit patterns is selected at random.
  • FIG. 6 is a view for explaining the first printing operation according to the first embodiment.
  • a region (printing region corresponding to the entire nozzle width of the printhead) printable by one scanning operation using all the ink orifices of the printhead is printed by four scanning operations in accordance with 4-bit image data of one pixel (multi-pass printing).
  • FIGS. 7A to 7C are views for explaining a dot layout (ink droplet adhering position) pattern within one pixel at a resolution of 600 ⁇ 600 dpi for pixel data printed by printing operation shown in FIG. 6 .
  • FIG. 7A shows 4-bit pixel data of bit data “a” to “d”.
  • FIG. 7B shows a state in which a dot is laid out at an upper left position “a” when a lattice of 600 ⁇ 600 dpi is segmented into 2 ⁇ 2 lattices of 1,200 ⁇ 1,200 dpi.
  • FIG. 7C shows dots laid out at the position “a” in accordance with the quantization level. In the first printing operation, a dot layout pattern as shown in FIG. 7C corresponding to pixel quantization is assigned to each pixel.
  • a printing medium is conveyed in the sub-scanning direction by a conveyance amount of 2/600 inches corresponding to 1 ⁇ 4 of the entire nozzle width. Only data at the bit position “a” out of the pixel data in FIG. 7A is selected and printed using orifices n 7 and n 8 of the printhead for an image region I. More. specifically, the discharge timing of the printhead in the main scanning direction is a timing dischargeable at a resolution which is twice a resolution corresponding to 1 ⁇ 2 of a 600-dpi printing pixel in the main scanning direction.
  • Printing is done in the forward direction along the main scanning direction while ink is discharged only at the first half of the discharge timing corresponding to 1 ⁇ 2 of the 600-dpi printing pixel in the main scanning direction. In this manner, a printing dot is laid out and printed for each pixel at the position “a” in FIG. 7B .
  • the printing medium P is conveyed in the sub-scanning direction by a conveyance amount of 2/600 inches.
  • Only data at the bit position “b” out of the pixel data in FIG. 7A is selected and printed using orifices n 5 and n 6 for the image region I and the orifices n 7 and n 8 for an image region II. More specifically, printing is done in the forward direction along the main scanning direction while ink is discharged to the same lattice point as that in the first scanning operation only at the first half of the discharge timing corresponding to 1 ⁇ 2 of the 600-dpi printing pixel in the main scanning direction. A printing dot is laid out and printed for each pixel at the position “a” in FIG. 7B .
  • the printing medium P is conveyed in the sub-scanning direction by a conveyance amount of 2/600 inches.
  • Only data at the bit position “c” out of the pixel data in FIG. 7A is selected and printed using orifices n 3 and n 4 for the image region I, the orifices n 5 and n 6 for the image region II, and the orifices n 7 and n 8 for the image region III. More specifically, printing is done in the forward direction along the main scanning direction while ink is discharged to the same lattice points as those in the first and second scanning operations only at the first half of the discharge timing corresponding to 1 ⁇ 2 of the 600-dpi printing pixel in the main scanning direction. A printing dot is laid out and printed for each pixel at the position “a” in FIG. 7B .
  • the printing medium P is conveyed in the sub-scanning direction by a conveyance amount of 2/600 inches.
  • Only data at the bit position “d” out of the pixel data in FIG. 7A is selected and printed using orifices n 1 and n 2 for the image region I, the orifices n 3 and n 4 for the image region II, the orifices n 5 and n 6 for the image region III, and the orifices n 7 and n 8 for the image region IV.
  • printing is done in the forward direction along the main scanning direction while ink is discharged to the same lattice points as those in the first to third scanning operations only at the first half of the discharge timing corresponding to 1 ⁇ 2 of the 600-dpi printing pixel in the main scanning direction.
  • a printing dot is laid out and printed for each pixel at the position “a” in FIG. 7B .
  • Printing is performed in the fifth and subsequent scanning operations by the same method as that of the first to fourth scanning operations.
  • FIGS. 8A to 8D are views each showing the dot distribution of 2 ⁇ 2 pixels printed by the first printing operation in correspondence with each quantization level.
  • FIG. 8A shows quantization level 1
  • FIG. 8B shows quantization level 2
  • FIG. 8C shows quantization level 3
  • FIG. 8D shows quantization level 4 . From FIGS. 8A to 8D , dots are laid out at the same interval at any level.
  • FIG. 9 is a view for explaining a second printing operation according to the first embodiment.
  • a region printable by one scanning operation using all the ink orifices of the printhead is printed by four scanning operations in accordance with 4-bit image data of one pixel (multi-pass printing).
  • FIGS. 10A to 10C are views for explaining a dot layout (ink droplet adhering position) pattern within one pixel at a resolution of 600 ⁇ 600 dpi for pixel data printed by printing operation shown in FIG. 9 .
  • FIG. 10A shows 4-bit pixel data of bit data “a” to “d”.
  • FIG. 10B shows a state in which dots are laid out at an upper left position “a” and lower left position “b” when a lattice of 600 ⁇ 600 dpi is segmented into 2 ⁇ 2 lattices of 1,200 ⁇ 1,200 dpi.
  • FIG. 10C shows dots laid out at the positions “a” and “b” in accordance with the quantization level. In the second printing operation, a dot layout pattern as shown in FIG. 10C corresponding to pixel quantization is assigned to each pixel.
  • quantization level 1 has two dot layout (ink droplet adhering position) patterns
  • quantization level 2 has three dot layout patterns
  • quantization level 3 has four dot layout patterns
  • quantization level 4 has five dot layout patterns.
  • Only data at the bit position “a” out of the pixel data in FIG. 10A is selected and printed using the orifices n 7 and n 8 of the printhead for the image region I. More specifically, printing is done in the forward direction along the main scanning direction while ink is discharged only at the first half of the discharge timing corresponding to 1 ⁇ 2 of the 600-dpi printing pixel in the main scanning direction.
  • a printing dot is laid out and printed for each pixel at the position “b” in FIG. 10B .
  • Only data at the bit position “b” out of the pixel data in FIG. 10A is selected and printed using the orifices n 5 and n 6 for the image region I and the orifices n 7 and n 8 for the image region II. More specifically, printing is done in the forward direction along the main scanning direction while ink is discharged to a position shifted from the dot printing position of the first scanning by 1/1200 inches in the sub-scanning direction only at the first half of the discharge timing corresponding to 1 ⁇ 2 of the 600-dpi printing pixel in the main scanning direction. A printing dot is laid out and printed for each pixel at the position “a” in FIG. 10B .
  • Only data at the bit position “c” out of the pixel data in FIG. 10A is selected and printed using the orifices n 3 and n 4 for the image region I, the orifices n 5 and n 6 for the image region II, and the orifices n 7 and n 8 for the image region III. More specifically, printing is done in the forward direction along the main scanning direction while ink is discharged to only the same lattice point as that in the first scanning operation only at the first half of the discharge timing corresponding to 1 ⁇ 2 of the 600-dpi printing pixel in the main scanning direction. A printing dot is laid out and printed for each pixel at the position “b” in FIG. 10B .
  • Only data at the bit position “d” out of the pixel data in FIG. 10A is selected and printed using the orifices n 1 and n 2 for the image region I, the orifices n 3 and n 4 for the image region II, the orifices n 5 and n 6 for the image region III, and the orifices n 7 and n 8 for the image region IV.
  • printing is done in the forward direction along the main scanning direction while ink is discharged to only the same lattice point as that in the second scanning operation only at the first half of the discharge timing corresponding to 1 ⁇ 2 of the 600-dpi printing pixel in the main scanning direction.
  • a printing dot is laid out and printed for each pixel at the position “a” in FIG. 10B .
  • Printing is performed in the fifth and subsequent scanning operations by the same method as that of the first to fourth scanning operations.
  • FIGS. 11A to 11D are views each showing the dot distribution of 2 ⁇ 2 pixels printed by the second printing operation in correspondence with each quantization level.
  • FIG. 11A shows quantization level 1
  • FIG. 11B shows quantization level 2
  • FIG. 11C shows quantization level 3
  • FIG. 11D shows quantization level 4
  • dots are laid out at different intervals at any level. In these dot layouts, all upper left and lower right pixels are printed at the position “a” in FIG. 10B , and all upper right and lower left pixels are printed at the position “b” in FIG. 10B in a matrix of 2 ⁇ 2 pixels at 600 ⁇ 600 dpi shown in FIGS. 11A to 11D .
  • FIG. 12 is a table showing the relationship among the main scanning sizes of printing media printed by the first and second printing operations, density unevenness in the main scanning and sub-scanning directions, and graininess.
  • the quality of a printed image is evaluated at five levels. “ ⁇ ” means “excellent”, “ ⁇ ” means “good”, “ ⁇ ” means “fair”, “x” means “not good”, and “xx” means “bad”.
  • Density unevenness is suppressed for a smaller printing medium size, and graininess is suppressed for a larger printing medium size.
  • Density unevenness hardly stands out for a smaller printing medium size because the generation period of density unevenness visually relatively prolongs for a smaller printing medium size, and the number of sparse and dense patterns suffering density unevenness decreases. Graininess is reduced for a larger printing medium size because the greater the visual distance from the printing medium becomes the higher the spatial frequency visually becomes.
  • the first printing operation will be examined.
  • density unevenness in the main scanning and sub-scanning directions exhibits good level when the main scanning size of the printing medium is 4 inches or less.
  • the image quality is no longer good, and density unevenness becomes notable.
  • the first printing operation uses only one dot layout pattern (see FIG. 7C ) as a dot layout pattern corresponding to each quantization level.
  • periodic density unevenness is originally conspicuous.
  • the density unevenness level cannot be permitted.
  • not only graininess is suppressed as the main scanning size of the printing medium increases, but also it is still sufficiently suppressed even for a small-size printing medium.
  • the second printing operation density unevenness in the main scanning and sub-scanning directions exhibits good level regardless of the main scanning size of the printing medium. That is, the second printing operation uses plural types of dot layout patterns (see FIG. 10C ) as a dot layout pattern corresponding to each quantization level. Noise is originally added, and periodic density unevenness originally hardly stands out. Even for a large-size printing medium on which density unevenness tends to be conspicuous, density unevenness is sufficiently reduced, and the density unevenness level is satisfactorily good. To the contrary, graininess is slightly worse than that in the first printing operation because printing dots are laid out at different intervals at any quantization level, as shown in FIGS. 11A to 11D , in other words, noise is inherently added. As the main scanning size of the printing medium decreases, the visual distance from the printing medium becomes smaller. Thus, graininess stands out for a small-size printing medium.
  • the graininess level is no longer good when the size of the printing medium is 4 inches or less. Considering these matters, when the second printing operation is adopted for a relatively-small-size printing medium, density unevenness is suppressed, but graininess becomes conspicuous. When the second printing operation is adopted for a relatively-large-size printing medium, an image in which both density unevenness and graininess are suppressed can be printed.
  • the first printing operation is executed when the size of the printing medium used for printing is 4 inches or less.
  • the second printing operation is executed when the size of the printing medium used for printing is larger than 4 inches.
  • This can suppress both density unevenness and graininess in the main scanning and sub-scanning directions to acceptable levels.
  • one dot layout pattern (pattern as shown in FIG. 7C ) is assigned to a plurality of pixels at the same quantization level for a relatively small printing medium size.
  • different dot layout patterns are assigned to a plurality of pixels at the same quantization level. Both the density unevenness suppression effect and graininess suppression effect can be obtained regardless of the printing medium size.
  • FIG. 13 is a flow chart showing printing control according to the first embodiment.
  • step S 1301 whether the main scanning size of the printing medium is 4 inches or less is determined on the basis of information on a printing medium size necessary for printing that is added to image data input to the image input unit 303 .
  • step S 1301 the processing advances to step S 1302 to perform printing by the first printing operation, and then to step S 1303 . If NO in step S 1301 , the processing advances to step S 1304 to perform printing by the second printing operation, and then to step S 1303 .
  • step S 1303 whether or not image data of the next page or next job exists is determined. If YES in step S 1303 , the processing returns to step S 1301 to repeat the above-described processing; if NO, the processing ends.
  • the ink droplet adhering position as a dot layout within each printing pixel on a printing medium is changed in accordance with the main scanning size of the printing medium. This results in printing a high-quality image in which density unevenness is sufficiently suppressed and graininess is visually reduced.
  • the printing medium conveyance amount in the sub-scanning direction is changed every scan-printing.
  • the present invention is not limited to this.
  • the printing medium conveyance amount may be set equal to that in the first printing operation, and instead, the ink droplet discharge timing of the printhead may be changed in the main scanning direction in which the printhead is scanned.
  • FIGS. 14A to 14C are views for explaining a printing dot layout (ink droplet adhering position) pattern within each printing pixel on a printing medium when pixel data shown in FIG. 5 is printed with the same conveyance amount as that in the first printing operation by changing the ink droplet discharge timing of the printhead in the main scanning direction.
  • a printing dot layout ink droplet adhering position
  • FIG. 14A shows 4-bit pixel data of bit data “a” to “d”.
  • FIG. 14B shows a state in which dots are laid out at an upper left position “a” and upper right position “b” when a lattice of 600 ⁇ 600 dpi is segmented into 2 ⁇ 2 lattices of 1,200 ⁇ 1,200 dpi.
  • FIG. 14C shows dots laid out at the positions “a” and “b” in accordance with the quantization level. In printing operation of a first modification, a dot layout pattern as shown in FIG. 14C corresponding to pixel quantization is assigned to each pixel.
  • quantization level 1 has two dot layout (ink droplet landing position) patterns
  • quantization level 2 has three dot layout patterns
  • quantization level 3 has four dot layout patterns
  • quantization level 4 has five dot layout patterns.
  • a printing medium is conveyed in the sub-scanning direction by a conveyance amount of 2/600 inches corresponding to 1 ⁇ 4 of the entire nozzle width of the printhead. Only data at the bit position “a” out of the pixel data in FIG. 14A is selected and printed using the orifices n 7 and n 8 of the printhead for the image region I. More specifically, the discharge timing of the printhead in the main scanning direction is a timing dischargeable at a resolution which is twice a resolution corresponding to 1 ⁇ 2 of a 600-dpi printing pixel in the main scanning direction.
  • Printing is done in the forward direction along the main scanning direction while ink is discharged only at the first half of the discharge timing corresponding to 1 ⁇ 2 of the 600-dpi printing pixel in the main scanning direction.
  • a printing dot is laid out and printed for each pixel at the position “a” in FIG. 14B .
  • the printing medium P is conveyed in the sub-scanning direction by a conveyance amount of 2/600 inches.
  • Only data at the bit position “b” out of the pixel data in FIG. 14A is selected and printed using the orifices n 5 and n 6 for the image region I and the orifices n 7 and n 8 for the image region II. More specifically, printing is done in the forward direction along the main scanning direction while ink is discharged to a position shifted from the dot printing position of the first scanning by 1/1200 inches in the main scanning direction at only the second half of the discharge timing corresponding to 1 ⁇ 2 of the 600-dpi printing pixel in the main scanning direction and a discharge timing different from that of the dot printing position in the first scanning.
  • a printing dot is laid out and printed for each pixel at the position “b” in FIG. 14B .
  • the printing medium P is conveyed in the sub-scanning direction by a conveyance amount of 2/600 inches.
  • Only data at the bit position “c” out of the pixel data in FIG. 14A is selected and printed using the orifices n 3 and n 4 for the image region I, the orifices n 5 and n 6 for the image region II, and the orifices n 7 and n 8 for the image region III. More specifically, printing is done in the forward direction along the main scanning direction only at the first half of the discharge timing corresponding to 1 ⁇ 2 of the 600-dpi printing pixel in the main scanning direction and a timing at which ink is discharged to the same lattice point as in the first scanning. A printing dot is laid out and printed for each pixel at the position “a” in FIG. 14B .
  • the printing medium P is conveyed in the sub-scanning direction by a conveyance amount of 2/600 inches. Only data at the bit position “d” out of the pixel data in FIG. 14A is selected and printed using the orifices n 1 and n 2 for the image region I, the orifices n 3 and n 4 for the image region II, the orifices n 5 and n 6 for the image region III, and the orifices n 7 and n 8 for the image region IV.
  • printing is done in the forward direction along the main scanning direction while ink is discharged at only the second half of the discharge timing corresponding to 1 ⁇ 2 of the 600-dpi printing pixel in the main scanning direction and the same timing as that in the second scanning.
  • a printing dot is laid out and printed for each pixel at the position “b” in FIG. 14B .
  • Printing is performed in the fifth and subsequent scanning operations by the same method as that of the first to fourth scanning operations.
  • FIGS. 15A to 15D are views each showing the dot distribution of 2 ⁇ 2 printed pixels in correspondence with each quantization level according to the first modification.
  • FIG. 15A shows quantization level 1
  • FIG. 15B shows quantization level 2
  • FIG. 15C shows quantization level 3
  • FIG. 15D shows quantization level 4
  • dots are laid out at different intervals at any level. In these dot layouts, all upper left and lower right pixels are printed at the position “a” in FIG. 14B , and all upper right and lower left pixels are printed at the position “b” in FIG. 14B in a matrix of 2 ⁇ 2 pixels at 600 ⁇ 600 dpi shown in FIGS. 15A to 15D .
  • printing dots are laid out at different intervals in the sub-scanning direction in FIGS. 11A to 11D , but laid out at different intervals in the main scanning direction in FIGS. 15A to 15D .
  • the printing dot layout (ink droplet adhering position) within each printing pixel is changed in accordance with the main scanning size of the printing medium.
  • the present invention is not limited to this.
  • the printing dot layout (ink droplet adhering position) within each printing pixel may be changed in accordance with the sub-scanning size of the printing medium.
  • the printing dot layout (ink droplet adhering position) within each printing pixel may be changed in accordance with the sum of the main scanning and sub-scanning sizes of the printing medium.
  • FIG. 16 is a table showing the relationship among the sub-scanning size of the printing medium, density unevenness in the main scanning and sub-scanning directions, and graininess according to the second modification.
  • FIG. 16 shows image quality results obtained by printing while changing the printing dot layout within each printing pixel in accordance with the sub-scanning size of the printing medium.
  • FIG. 17 is a table showing the relationship among the sum of the main scanning and sub-scanning sizes of the printing medium, density unevenness in the main scanning and sub-scanning directions, and graininess according to the second modification.
  • FIG. 17 shows image quality results obtained by printing while changing the printing dot layout within each printing pixel in accordance with the sum of the main scanning and sub-scanning sizes of the printing medium.
  • the second embodiment will exemplify a case in which the ink droplet adhering position within each printing pixel on a printing medium is changed in accordance with the printing size of image data to be printed.
  • a printhead adopted in the second embodiment is identical to one having the arrangement shown in FIG. 4 .
  • the quantization level of image data, the number of printing dots, and pixel data are also the same as those shown in FIG. 5 .
  • the first and second printing operations are the same as those shown in FIGS. 6 and 9 .
  • the printing dot layouts and the like are also the same as those shown in FIGS. 7A to 7C and 8 A to 8 D for the first printing operation, and those shown in FIGS. 10A to 10C and 11 A to 11 D for the second printing operation.
  • FIG. 18 is a table showing the relationship among the main scanning sizes of image data printed on printing media by the first and second printing operations, density unevenness in the main scanning and sub-scanning directions, and graininess.
  • the second printing operation reduces periodic density unevenness in comparison with the first printing operation because noise is added by laying out printing dots at different intervals.
  • the density unevenness period relatively increases. Even in the first printing operation, density unevenness hardly visually stands out when the size of the printing image is about 4 inches or less.
  • the second printing operation generates more graininess than the first printing operation because printing dots are laid out at different intervals.
  • the main scanning size of the printing image increases, the visual distance from a printing medium on which the image is printed increases, thereby reducing perceptible graininess.
  • graininess hardly visually stands out when the size of the printing image is larger than 4 inches.
  • the first printing operation is executed when the main scanning size of the printing image is 4 inches or less.
  • the second printing operation is executed when the main scanning size of the printing image is larger than 4 inches.
  • one dot layout pattern (pattern as shown in FIG. 7C ) is assigned to a plurality of pixels at the same quantization level for a relatively small image data size.
  • different dot layout patterns are assigned to a plurality of pixels at the same quantization level. Therefore, both the density unevenness suppression effect and graininess suppression effect can be obtained regardless of the printing medium size.
  • FIG. 19 is a flow chart showing printing control according to the second embodiment.
  • step S 2001 whether the maximum printing size of an image to be printed in the main scanning direction is 4 inches or less is determined on the basis of image data input to the image input unit 303 .
  • step S 2001 the processing advances to step S 2002 to perform printing by the first printing operation, and then to step S 2003 . If NO in step S 2001 , the processing advances to step S 2004 to print by the second printing operation, and then to step S 2003 .
  • step S 2003 whether or not image data of the next page or next job exists is determined. If YES in step S 2003 , the processing returns to step S 2001 to repeat the above-described processing; if NO, the processing ends.
  • the ink droplet adhering position as a dot layout within each printing pixel on a printing medium is changed in accordance with the main scanning size of an image to be printed on the basis of image data (i.e., the main scanning size of image data). This results in printing a high-quality image in which density unevenness is sufficiently suppressed and graininess is visually reduced.
  • the printing medium conveyance amount in the sub-scanning direction is changed every scan-printing in the second printing operation, unlike the first printing operation.
  • the printing medium conveyance amount may be set equal to that in the first printing operation, and the ink droplet discharge timing of the printhead may be changed in the main scanning direction in which the printhead is scanned.
  • the printing dot layout (ink droplet adhering position) within each printing pixel is changed in accordance with the main scanning size of the printing image (main scanning size of image data).
  • the present invention is not limited to this.
  • the printing dot layout (ink droplet adhering position) within each printing pixel may be changed in accordance with the sub-scanning size of the printing image.
  • the printing dot layout (ink droplet adhering position) within each printing pixel may be changed in accordance with the sum of the main scanning and sub-scanning sizes of the printing image.
  • FIG. 20 is a table showing the relationship among the sub-scanning size of an image printed on a printing medium, density unevenness in the main scanning and sub-scanning directions, and graininess.
  • FIG. 20 shows image quality results obtained by printing while changing the printing dot layout within each printing pixel in accordance with the sub-scanning size of the printing medium.
  • FIG. 21 is a table showing the relationship among the sum of the main scanning and sub-scanning sizes of the printing image, density unevenness in the main scanning and sub-scanning directions, and graininess.
  • FIG. 21 shows image quality results obtained by printing while changing the printing dot layout within each printing pixel in accordance with the sum of the main scanning and sub-scanning sizes of the printing medium.
  • the first and second embodiments adopt a method of comparing the printing medium size or image data size with a predetermined size and changing the dot layout pattern for use in accordance with the comparison result (in other words, a method of selecting, in accordance with the comparison result, one printing operation from a plurality of printing operations of printing with different dot layouts).
  • the present invention is not limited to this.
  • Such comparison processing can also be omitted by making a dot layout pattern for use (printing operation method for use) correspond to a printing medium size or image data size in advance without comparing the printing medium size or image data size with a predetermined size.
  • a table which makes information on the printing medium size and a dot layout pattern for use correspond to each other may be prepared in advance. Upon printing, information on the printing medium size is acquired, and a dot layout pattern corresponding to the acquired information is used.
  • the table may be one which makes information on the image data size and a dot layout pattern for use correspond to each other, or one which makes information on the image data size, information on the printing medium size, and a dot layout pattern for use correspond to each other.
  • the size value such as 3 inches, 4 inches, or X inches is used as information on the printing medium size or information on the image data size.
  • Information suffices to correspond to the printing medium size or image data size, and may be information which indirectly represents the printing medium size or image data size.
  • the size information may be represented by 4-bit data such that “0000” is defined as 3 inches, “0001” is defined as 4 inches, and “0010” is defined as 5 inches.
  • Such information which indirectly represents the printing medium size or image data size may be employed.
  • image data the number of bits of image data and size information can also be made to correspond to each other.
  • information suffices to be information on the printing medium size and/or information on the image data size, and may be information which directly or indirectly represents the size.
  • either the first printing operation mode in which one dot layout pattern (e.g., dot layout pattern as shown in FIG. 7C ) is assigned to pixels at the same level in which the same number of dots are printed, or the second printing operation mode in which plural types of dot layout patterns (e.g., dot layout patterns as shown in FIG. 10C ) are assigned to pixels at the same level in which the same number of dots are printed is selected on the basis of at least either one of information on the printing medium size and information on the image data size.
  • these printing modes may be arbitrarily selected by the user.
  • the mode may be selected by a switch attached to the operation unit 306 of the printing apparatus.
  • the mode may be selected on property selection screen of a printer driver installed in a host computer connected to the printing apparatus.
  • the printhead used in the two embodiments described above has eight orifices at a resolution of 600 dpi in the sub-scanning direction, but the present invention is not limited to this.
  • the resolution may be 1,200 dpi or another density, and the number of orifices may be 64, 128, or 256 other than eight.
  • the orifice layout is not limited to one as shown in FIG. 4 .
  • FIG. 22 is a view showing a modification to the orifice layout of the printhead.
  • orifices may be staggered instead of a linear layout.
  • the size of an ink droplet discharged from each ink orifice is about 5 pl in the above embodiments, but the present invention is not limited to this.
  • the ink droplet size may be as small as about 2 pl, or as large as about 10 pl.
  • image data may be 8-bit data at a resolution of 600 ⁇ 600 dpi per pixel and quantized to nine levels from 0 to 8.
  • one of plural types of pixel data is selected at random at a quantization level corresponding to pixel data at which a plurality of bit patterns exist, as shown in FIG. 5 .
  • the present invention is not limited to this, and pixel data may be regularly selected.
  • the embodiments have described printing operation by referring to only one printhead.
  • the present invention can also be applied to four printheads which print in color using four, K, C, M, and Y inks, as shown in FIG. 1 , obtaining the same effects as those described above.
  • droplets discharged from the printhead are ink droplets
  • liquid stored in the ink tank is ink.
  • the liquid to be stored in the ink tank is not limited to ink.
  • processing liquid or the like to be discharged onto a print medium so as to improve the fixing property or water repellency of a printed image or its image quality may be contained in the ink tank.
  • the above embodiments preferably employ a method in which means (e.g., an electrothermal transducer or laser beam) for generating thermal energy as energy used to discharge ink is adopted and the ink state is changed by thermal energy.
  • means e.g., an electrothermal transducer or laser beam

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JP2004276596A (ja) 2004-10-07

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